The present invention relates to a voltage regulator.
In general, the quality of the spot-welded joints are dependent upon the Joule's heat applied to the metal pieces to be welded, that is the total heat generated in the work which is given by
(welding current).sup.2 .times. (resistance of and between the metal pieces to be joined and electrodes) .times. (time interval, during which the welding current flows).
It is seen from the above relation that the quality of the welded joints is especially dependent upon the welding current, since it is squared, so that when the welding current is maintained constant even if the supply voltage varies, the constant Joule's heat may be produced. Thus the quality of the welded joints may be much enhanced. However, a time interval during which the welding current flows is very short and is of the order to a few cycles to tens of cycles so that no satisfactory feedback can be attained in the closed loop automatic control system because a time interval longer than tens of cycles must be tolerated to respond to the error or variation in supply voltage.
There has been proposed a voltage regulator of the type in which the welding current which is detected by a current transformer, squared, integrated and multiplied by the welding current supply time interval may be maintained constant. However, this voltage regulator is of closed loop type so that no satisfactory result can be attained because of the control time delay. Furthermore, the voltage regulator of the type described is complex in circuitry and very expensive to manufacture so that it is not feasible in practice.